WiMAX is described in the IEEE 802.16 Wireless Metropolitan Area Network (MAN) standard. WiMAX allows for high-speed wireless data transmissions over long distances.
The core components of an 802.16 network are base stations (BS) and subscriber stations ((SS), sometimes referred to as mobile stations (MS)). The IEEE 802.16-2005 standard (formerly named but still known as IEEE 802.16e or Mobile WiMAX) is designed to support Point-to-Multipoint (PMP).
In PMP mode, the BS and one or more SS's are organized into a cellular-like structure. This type of network requires that all SS be within the transmission range and clear line of sight of the BS which uses an omnidirectional antenna. The BS controls activity within the cell, including access to the network by a SS, and allocations to achieve quality of service (QoS). FIG. 1A is a pictorial view of a PMP network in which BS 50 is in PMP communication with SS 52, SS 53, SS 54 and SS 55. FIG. 1B is a schematic diagram of a very simple PMP network in which BS 12 is in point-to-multipoint communication with both SS 14 and SS 16.
But in cellular-like PMP mode, there are many limitations such as cell transmission coverage, frequency re-use, power consumption, system capacity and performance beyond the boundaries of the BS coverage area. These limitations would cause signal degradation such as path loss, shadowing, and increase the complexity for handover in a large scale and high-speed mobility environment.